The present invention refers to an apparatus for filling valved sacks, and in particular to a filling machine of the type having at least one filling pipe which is in fluid communication with a feed unit.
Filling machines for valved sacks come in various configurations e.g. as so-called rotary filling machines and stationary machines. In general, one end of the filling pipe constitutes the outlet port through which the material is discharged and introduced into the valved sack while the other end of the filling pipe is provided with a connection flange for attachment to the feed unit and for allowing a simple exchangeability thereof. In rotary filling machines, the filling pipes run either horizontal or vertical or are inclined relative to the horizontal by a small acute angle. Stationary filling machines can be designed in like manner if configured in form of a serial packaging machine.
Feed units for filling machines include e.g. rotatable feed turbines or pneumatically operated feed pots, called air packers. German patent DE-PS 3,607,508 describes a rotary filling machine for valved sacks which is equipped with an air packer and a feed turbine and can be combined with different types of filling pipes. In many cases, the use of double-walled filling pipes is preferred in order to enable a ventilation of the sacks during a filling operation. An exemplified double-walled filling pipe is disclosed e.g. in German patent DE-PS 3,834,810 which discloses also the arrangement of a reciprocating plunger for securing a valved sack being placed onto to filling pipe.
Common to these conventional filling machines for valved sacks is the drawback that air exiting from the sack carries with it material to be filled in the valved sack. This is true in particular when powdered materials are concerned. The escape of powdered particles or dust is annoying to the operator and results in an increased loss of material and thus in higher costs.
Several attempts were undertaken to avoid these drawbacks, none of which was able to satisfactorily solve the problem. One such attempt proposed a conical or double-cone configuration of the filing pipe. Even though such design improved the filling operation of valved sacks, the manufacture of valved sacks becomes more complicated and results in increased costs as the valve of the valved sack necessitates a complementary conical configuration.
In general, the attachment of a valved sack to the filling pipe should be possible in an easy manner without requiring any particular force or effort. For that reason, a play exists between the inner contour of the valve and the filling pipe. Since the presence of such a play actually promotes the escape of material, the conical design of the filling pipe was proposed in order to effectively act as a sealing element in the area of the valve. The conical configuration of the filling pipe allows a reduction in the amount of escaping material; however, a complete sealing is not ensured since the valve of the sack expands during the filling operation by the pressure of the material flowing into the valved sack. With the double-cone design of the filling pipe, the amount of escaping material could further be reduced, however, the increasing need for a dust-free and clean filling operation could still not be met. Moreover, it is unavoidable in the production of valved sacks that the generally tubular valves lie outside admissable tolerances. This further complicates the possibility of reaching a dust-free and clean filling operation.
Other solutions for reducing an escape of dust particles encompass filling pipes with expandable packing, or split filling pipes which open up in a jaw-like or beak-like manner. In the latter case, passages are however created after opening of both parts of the filling pipes through which material can escape. Moreover, outgoing air cannot be guided in a closed system.
It was further proposed to design the filling pipe at least in the central area thereof as an expandable tube. Apart from the fact that such an expandable tube constitutes a wearing part, the attachment of valved sacks is complicated because the slidability of the tube relative to the normal filling pipes is disadvantageous.
In accordance with another proposal, the valve of the valved sacks is designed in form of a filter valve made of air-permeable material through which outgoing air is aspirated. Also this solution does not satisfactorily solve the problem of widening of the valve during filling operation.
German patent DE-PS 580,335 discloses a feed nozzle which is flattened at the upper side either over the entire length of the nozzle or over the forward area thereof. Instead of being flattened, the feed nozzle may also be provided in the central area with a transverse indentation. Cooperating with the feed nozzle is a sack holder which is swingably mounted to press the sack against the feed nozzle during filling operation. In order to increase the friction, the flattened area of the filling pipe is roughened, with the complimentary side of the sack holder being roughened as well. Instead of roughening, the filling pipe may also be provided at a central area thereof with a step or an indentation so that the sack becomes deformed by the sack holder. This publication is silent in regard with an escape of material and with the structure of a filling machine to allow filling material to pass through the feed nozzle into the sack. Moreover, the provision of a transverse step or indentation is insufficient to attain a sufficient sealing; rather, passages are created through which material can escape.